U.S. Pat. Nos. 3,513,848 to Winston et al., U.S. Pat. No. 4,662,068 to Polonsky, and U.S. Pat. No. 5,383,883 to Wilk et al. describe joining surgical suture by welding or fusing strands together. The present invention includes significant advances over the prior art.
First among these is control of critical parameters affecting the strength properties of the weld. Principal among these is the force with which the ultrasonic element is brought to bear against the material to be welded. Winston et al. describe a device where this force is provided by the user through pressure applied by the thumb and forefingers. This method of pressure control is subject to substantial variation from weld to weld and from user to user. Similarly, Polonsky and Wilk et al. describe scissors handled instruments with pivoting jaws that apply pressure proportional to the hand pressure of the user. Another critical control parameter is the amount of energy imparted to the weld. Too much energy imparted to the weld would result in complete melting of the weld region, resulting in an amorphous mass of greatly reduced strength. Similarly, too little energy would result in a reduced or absent weld area, also resulting in reduced weld strength. Here again Winston et al., Polonsky and Wilk et al. provide only for timed energy input at the discretion of the user and therefore subject to substantial variation.
Another advance of the present invention over the prior art is the inclusion of means for controlling the morphology of the material in the weld region to produce welds of significantly greater strength than those produced by the apparatus and method described by Winston et al., Polonsky and Wilk et al. Our experience has shown that welds of superior strength are created when the following conditions are satisfied: 1) The weld is configured as a lap weld with load applied from opposite ends of the long axis of the weld (i.e., loaded in shear, not in peel) 2) the area of the welded region is large, 3) a substantial portion of the suture on either side of the weld area has not been subjected to sufficient heat to reduce the tensile strength of the material, and 4) there is a gradual transition from the stressed full cross section of material outside the weld region to the point where the maximum proportion of cross section has been sacrificed to melting to form the weld. Polonsky and Wilk et al. describe the exiting ends of the suture being welded in an orientation such that loads placed upon the suture would subject the weld to peeling stress. Winston et al. describe welds that would load in peel and others in shear, however those loaded in shear are formed by crossing the suture, a practice resulting in weld areas limited to the small region where the segments overlap in a crosswise fashion. Similarly, Polonsky and Wilk et al. refer to twisting the suture, yielding the same end result as crossing the strands. In order to preserve a non-melted (and therefore non-weakened) portion of the material cross section outside of the weld area, melting must be localized to the region where the overlapping segments of suture abut each other. This condition is best accomplished in ultrasonic welding a lap joint when the two segments to be joined are acoustically coupled to structures that vibrate relative to each other. Experience has shown that acoustic coupling is best accomplished by large areas of contact with the vibrating and non-vibrating or counter-vibrating structures. Winston et al describe "welding tips having a small area of contact" and Winston et al., Polonsky and Wilk et al. show flat welding surfaces in contact with round suture, a situation resulting in thin, line contact of a small area. The present invention includes surfaces which conform to the suture to maximize acoustic coupling. A further advance over Winston et al., Polonsky and Wilk et al. is the inclusion of means to facilitate loading suture into the device in an orientation conducive to optimum weld characteristics in vivo. Winston et al., Polonsky and Wilk et al. require the user to cross or twist the suture and place it into a slot in the device. This maneuver is difficult to perform in laparoscopic surgery and would likely require withdrawing the suture ends and the instrument from the body cavity for suture loading. In the present invention, suture ends need only be held under slight tension and a simple grab-twist-grab motion employed to load the suture. Another advantage of the present invention over Winston et al is its means for releasing the finished stitch from the device without compressing tissue inside the stitch or stretching the suture material. The present invention also represents an advance over Winston et al. by including a welding apparatus structure constructed with an elongated shaft suitable for use in minimally invasive surgery (MIS) where suturing must be performed internally through a small incision, or where the instrument must be introduced through a tubular structure. Further advances over Winston et al. and Wilk et al. include a means for cutting the exiting ends of the suture.
It is an object of the present invention to provide an instrument for joining lengths of polymer suture material in areas of difficult or limited access, such as in minimally invasive surgery (MIS).
It is a further object of the present invention to provide an instrument with means to provide a stitch for tissue approximation wound closure, ligating, attachment or suture anchoring functions.
It is a further object of the present invention to provide an instrument with means to provide an attached structure with exiting strands to be used for further tissue approximation, wound closure, ligating, attachment or suture anchoring functions.
It is a further object of the present invention to provide an instrument with means to facilitate loading suture material strands in areas of difficult or limited surgical access.
It is a further object of the present invention to provide an instrument with means for releasing joined surgical suture loops without stretching the loop or compressing the tissue material within the loop.
It is a further object of the present invention to provide an instrument with means for facilitating sliding passage of at least one of the suture material strands exiting a loop to facilitate tensioning of the loop.
It is a further object of the present invention to provide an instrument with means for clamping or securing one suture material strand exiting a loop to facilitate tensioning of the loop by pulling on the remaining, non-secured strand.
It is a further object of the present invention to provide an instrument with means for cutting one or more of the strands of suture material exiting the tensioned, joined, finished loop.
It is a further object of the present invention to provide an instrument with means for shielding the tissue to be sutured from direct contact with the vibrating ultrasonic member, thereby protecting the tissue from injury.
It is a further object of the present invention to provide an instrument with means for removing and replacing tissue contacting portions of the device to assist in maintaining sterility through disassembly for cleaning, or disposal and replacement of the tissue contaminated elements.
It is a further object of the present invention to provide an instrument with means for controlling the force with which the segments of material to be welded are held together before, during and after the welding process.
It is a further object of the present invention to provide an instrument with means for controlling the total weld energy imparted to the segments to be welded.